For example, when an alternator is driven by a crankshaft of an automotive engine via a belt, a pulley unit, etc., a pulsating change in rotation (a change in acceleration during rotation) may be generated on the crankshaft as a result of repetition of induction, compression, combustion and expansion, and exhaust strokes. When such a change in rotation is generated, an excessive rotating torque (torsion) or tension may be generated on a pulley, a rotating shaft or the belt. As an example, there is a tendency that the rotation of the crankshaft drops momentarily on the compression stroke or the like. However, since the alternator has large inertia, its rotating shaft cannot follow immediately the drop in rotation of the crankshaft (an alternator pulley), and an excessive rotating torque is generated between the rotating shaft and the pulley. As a result, the belt is pulled in a direction in which the torque is generated and a change in tension is produced, which may produce an overload in the belt or may reduce life of the belt. Then, with a view to preventing the production of the overload in the belt or the reduction in life of the belt, there has been known a technique in which a spring type one-way clutch and a torsion coil spring are interposed between a pulley and a rotating shaft (for example, see WO98/50709 (JP-T-2001-523325)).
According to the technique of WO98/50709, as is shown in FIG. 9, an overload produced in a belt by such a change in rotation as described above can be reduced by interrupting power by a spring type one-way clutch 76 or torsion deforming a torsion coil spring 74 in an elastic fashion. In WO98/50709, power from an engine is transmitted along a path from a pulley 106 to a shaft 36 via the spring type one-way clutch 76 and the torsion coil spring 74. In addition, an inner circumferential surface of the pulley 106 and the torsion coil spring 74 (an outer circumferential surface of an outer sleeve 64) are connected together so as to enable a circumferential relative displacement by a sleeve bushing 112 which is interposed therebetween. Because of this, every time power is interrupted by the clutch 76, the sleeve bushing 112 is subjected to rotational sliding of the outer sleeve 64 to wear, and there may be a case in which the sleeve bushing 112 is broken.